1. Field of the Invention
This invention relates generally to apparatus for preparing bacterial specimens and more particularly to automated apparatus of this type which prepares the specimens for visual counting, typing and other analysis of the bacterial populations.
2. Description of the Prior Art
One of the many procedures which must be performed in microbiology are plate streaks for isolating microbiological colonies. Distinctly isolated colonies are produced as a result of growth starting with a single cell. The isolated colonies are absolutely necessary for the observance of colony morphology and for the performance of staining and other procedures which are necessary for determining the genus and in many cases, the species, strain, etc. of an unknown organism. Both bacterial and fungus type micro-organisms must be isolated from test samples. In an actual process, a liquid such as isolation broths, blood, urine, etc. or solids such as feces, scrapings, etc. might be used to identify an unknown bacterial. Fungi requires the same type of isolation as bacteria but, unlike the bacterial, the fungi are generally not subjected to additional tests since colony characteristics and microscopic appearance alone are usually adequate for their identification.
Two or three plates are streaked per sample of each test specimen. The streaking process requires approximately 30 seconds per agar plate of a technologist's time. The quality of the streak and therefore the degrees of isolation of the microorganism depends upon the training received by the technologist and the care taken in performing the process.
Problems typically encountered during a streaking process include the use of an improperly cooled inoculating needle following flame sterilization. As a result, the organisms may be destroyed in the streaking process. In addition, contaminants may be introduced by the use of an improperly sterilized inoculating needle. There are also the problems caused by the lack of reproducibility of streaks from one technician to another and the difficulty a technician often encounters in streaking soft agars which are easily cut. An improperly made streak has to be redone before further testing is possible. The detection of a faulty streak may require anywhere from 12 to 48 hours depending upon the rate of growth of the organisms present in the sample.
Several machines have been developed for automatically preparing bacterial specimens. One such machine is disclosed in U.S. Pat. No. 3,778,351 which was granted on Dec. 11, 1973 to Robert J. Rosov. In this patent, means are provided for controlling relative movement of a specimen plate and a dispensing pipette. The volume rate of delivery of the specimen from the pipette to the specimen plate is accurately controlled in order to effect the preparation of the specimen along a pre-determined and reproducible pattern and concentration. Specifically, U.S. Pat. No. 3,778,351 provides a specimen plate having a plurality of laterally elongated grooves that are adapted to contain a bacterial specimen growth base material. The pipette is supported above the specimen plate which includes a frame, a table mounted on the frame for movement in one direction and indexing means on the table for engaging the specimen plate. The indexing means is movable relative to the table in a direction normal to the table movement for aligning each groove selectively with a pipette. As will be explained more fully hereinafter, U.S. Pat. No. 3,778,351 is contrasted from the present invention by virtue of the linear advance of the pipette and by a zig-zag path as opposed to a figure eight path.